Legionella, a waterborne bacterium, is one of the causative agents of nosocomial pneumonia. Results from mandatory reporting show that 17% of Legionnaires' disease cases in 1999 had stayed in a hospital or clinic, and that among them, 86% of nosocomial cases more often had a risk factor, compared to 70% for non-nosocomial cases. An initial circular from the Ministry of Health published in 1997 detailed the technical procedures for the surveillance and prevention of legionellosis. On December 31, 1998, a new circular reiterated the need to implement best practices for the maintenance of water systems in healthcare facilities and in establishments open to the public. To assess the measures taken regarding water systems and to manage the “Legionella” risk in accordance with the two aforementioned circulars, the CCLIN Paris-Nord coordinated an evaluation in private and public healthcare facilities across the Northern Interregion (Île-de-France, Nord-Pas-de-Calais, Picardy, Upper Normandy). R.A.